Multicomponent gas analyzer



Patented June 16, 1953 MULTICOMPNENT GAS ANALYZER John J. Heigl, Cranford, N. J., assigner to Standard Oil Development Company, a corporation of Delaware Application June I, 1950, Serial No. 165,401

This `invention relates to improved apparatus for the quantitative analytical determination of the constituents present in a multicomponent gas mixture. In one embodiment of this invention, apparatus is provided to -permit the infralred characterization of any desired number of infra-red absorbing constituents of a gaseous mixture. VIn Ia further embodimen-t of this invention, this general type of apparatus is employed in combination with a mass spectrometer, to persolaims. (oi. 25o-43.5)

mit the quantitative determina-tion of infra-red non-absorbing constituents as well.

This invention is related to the invention disclosed and claimed in U. S. patent application, Serial No.' 31,346, lecl -by Charles W. Skarstrom onV June 5, 1948. In the said application, improved infra-red analysis techniques are disclosed for the identification of any one infra-red absorbing gas in a mixture of gases. Thus, it is disclosed that infra-red analytical apparatus maybe so sensitized as to selectively determine one constituent ina mixture of infra-red absorbing gases. Towards this end it is disclosed that two beams of infra-red radiation are to be employed. One beam passes through the sample cell and through what may be called a lter cell to imping'e on one radiation detector. The second beam passes through a sample cell and through what may ybe called a compensator cell to impinge on a second radiation detector.

VIn addition the apparatus contains light intensity controls adapted to variably control, as desired, the quantity of radiation in each oi" the beams. By connecting the two r detectors in opposition and by providing suitable fluids in the lt'er and compensator cells, the differential detector output Ican be caused to depend solely on the' concentration of a particular constituent contained in a sample mixture.

' The general process and apparatus mentioned above is of yparticular application for the continuous analysis, or control of a process involving-streams yof hydrocarbon gases. Howevenit frequently happens that satisfactory controlcan only beobtained by the quantitative determination of more than one of the constituents present in a gas stream. When such information is required, it has heretofore been necessary to provide two infra-red yanalytical instruments of the character identied. Each of these instruments is then sensitized to permit the selective Idetermination of one given-component in Ithe mixture to be analyzed. It is apparent, however, that the necessity for multiplying the `analysis instruments in this manner is cumbersome, ineicient and expensive;-particularly in casesin which it is desirable, or necessary to determine 3, 4er more components in a mixture. Consequently,A i-t is the principal object of this invention to -provide greatly simplied apparatus simultaneously and continuously ydetermining any desired number of infra-red absorbing constituents in a gas mixture.

It is apparent thatA the general infra-red analytical techniques referred to heretofore, are of no utility for the analytical determination of nonabsorbing gas constituents. Consequently, it is a further object of this invention to employ a mass spectrometer in combination with infra-red analytical apparatus so as to permit the complete determination o-f both infra-red absorbing, and non-infra-red absorbing constituents of a gas mixture, The combination of -thespectrometer vand the infra-red absorbingxapparatus; is`

particularly desir-able, as uit permits a simple and effective discrimination between certain gases which have similar molecular weights-'but differing infra-red absorbing characteristics.

In accordance with this invention, therefore, infra-red analytical apparatus is provided having a plurality 4of sample cells. Thesesample cells are aligned with a plurality of lter and compensator cells, and la plurality of totally absorbent gas cells. The totally absorbent gas cellsV are pneumatically connected to a single detector, amplier, and recorder. By providing means to periodically control the passage of infra-red radiation successively through each of the iplurality of sample cells, itis 'possible to determine each of vthe infra-red absorbing constituents of a sample contained in, or passed through each of the sample cells. In addition the sample lto be analyzed is preferably passed through a mass spectrometer, to provide information as to not only 4the molecular Weights of gases in the mixture, butv also certain non-infra-red absorbing gases and thus to provide total information making possible the complete analysis of the gas mixture. 1 This invention may be fully understood by reference' to` the accompanying drawing which diagrammatically illustrates apparatus Yembodying the principles of this invention. The apparatos illustrated is suit-able' torr identifying the constituents of a gas mixture containing as many as six -idiiierent infra-red absorbing gases, and in addition containing any number of non-absorbing gases. l f Y As illustrated, the apparatus includes six sample cells, I' to 5, associated with the infra-red capable of characterization portion of the apparatus. In

' i addition a further sample cell is associated with the mass spectrometer diagrammatically indicated by the numeral 1. For the continuous analysis of a gas sample, gas is introduced to the system through line 8 and passes in series through each of the sample cells for eventual removal from the system through outlet 9 of the mass spectrometer 1. Associated with each of the sample cells, I through 6, is a source of infra-red energy, a rotating radiation blocking means, a lter cell, a compensator cell, andgas cells capable of substantially ing infra-red radiation reaching these cells. Thus, a lament I suitable for emitting infrared radiation is positioned adjacent to and aligned with each of the sample cells. The filament I0 is preferably in the form of a spiral adapted to emit a substantially uniform concentration of infra-red energy over the area dened by the ends of the sample cells. Positioned-between the iilament I0, and the adjacent sample cell, is a choppen This device may simply be a circular opaque plate provided with cutaway segments. This plate is rotated at a constant speed, for example, by means of a synchronized motor so that light is permitted to pass through the segments of the plate to reach the sample cell at a frequency of about 6 to cycles per second. -By this means the infrared'energy of the source I0 is caused to period-` icallypass through the sample cells.

Radiation fromthe lament I may be considered to pass vthrough each sample cell in two beams; that is, an upper beam passing through the upper portion of the sample cell, and a lower beam passing through the lower portion of the sample cell. A lter cell I2 is positioned in the upper beam of radiation passing through each of the sample cells, while Va compensator cell I3 is positioned in the lower beam of radiation passingthrough each of the sample cells. The filter and compensator cells are preferably of substantially identical construction so that each cell is of substantially the same cross-sectional area. Finally, the two beams of radiation having Vpassed through the lter cell`I2 or compencompletely absorby d tector I6. Similarly, gas lines lead from each of the cells I5 to a manifold line associated with a gas line I8 leading to the opposite side of the detector I5. 'Ihe detector I6 consists of a pressure detector of the condenser microphone type. This detector is sensitive to minute differences in pressure impressed across it by any differences in gas pressure existingin lines I'I' and i8. As condenser microphone detectors of this character are well known to the art, no further description will be made of this element of the apparatus.` VThe output of the condenser microphone detector I5 is conducted to an amplifier I9 which suitably amplifies the electrical output to operate a'recorder 20.

As heretofore described, operation of the gen- Y'eral apparatus described would result in the receipt of unintelligible signals from the detector as illustrated, the to sequentially operate sator cell I3 are directed towards the total absorption cells I4 and I5. Again, cells I4 andIS are of similar construction and have identical cross-sectional areas.

It is to be understood that each of the cells heretofore described are provided with suitable infrared transparent windows to permit the passage of infra-red energy through the cells. Thus, the cells may, for example, consist of rock salt, silver chloride, etc. It is preferred that light intensity controls I6 and I'I be positioned betweenv the lter and compensator cells, and the totally absorbent cells. Thus, one light intensity control I6 may be positioned in the upper beam of radiation between the cell I2 and I4, while a second light intensity control mai be positioned between cell I3 and I5 in the lower beam of radiation. The light intensity controls are simply opaque plates or shutters which may be so controlled as to vary the amount of radiation passing the controls, and reaching the cells I4 or I5.

' Each of the cells I4 and I5 are connected t0 pneumatic lines leading to the single detector assembly identified by the numeral I6. In particular, fluid lines leading from each of the cells I4 are connected to a manifold line associated with a gas line I1 on one side of the deand the recorder. To operatively employ the apparatus described, it is necessary that a sequence switching meansfbe provided adapted to sequentially control radiationA in conjunction' with each of the sample cells I to 6. This mai7 be done in a number ofY ways. One of the simplest is to employ a multicontact timing switch such as the timing switch 25 connected to the choppers II in such a manner as to periodchoppers on and off. Thus, timing switch 25 will 'operate ically switch these I'I associated with each of the sample-cells I Ito '6. This will havev the eiect of causingpulsating infra-red energy to first pass through sample Y cell I, to impinge on detectors I4 and I5 at'a time during which no pulsatinginfra-red energy is passed through any of the other sample cells. After a short interval the switch 25 will then discontinue transmission of the pulsating infra-red energy through sampleV cell I, and permit it to passY through sample cell 2, and in the same fashionrfor each of the other sample cells of the apparatus. The record of the detector outputs appearing on recorder 20 are preferably controlled by other contacts of theV timingswitch 25 to provide information as to which of the sample cellsv a particular portion of the record corresponds to. This rmay best be achieved by employing a recorder of the multipen type in which an individual pen will represent the output of each of the detectors associated with each of the sample cells.

It is possible to secure the necessary sequentialA operation` in other manners.Y For example, shutters 2B may be operated so as to have'the same effect.

In actually employing the apparatus described for analytical purposes, for example, in the analysis of a gas composition containing six infra-red absorbing gas constituents, the filter and compensator cells associated with each .of the six sample cells will be sensitized for selective determination of one of the six'gaseous components. Thus, for example, filter and compensator cells I2 and I3 associated with Ysample cell I will be sensitized for a constituent A contained in the mixture while the filter and compensator cells associated with samplecell 2'will be sensitized for a constituent B contained in the gas.

each rof the choppersl essary to critically adjust the trimmers I6 and,` I1.-1v ,associatedl with each ofl the sample cells.

Again, itr is Asometimes' desirable to provide an additional cell which may be called an interference cell positioned so that both of the beams of energyformerly refer-red to ,pass through the interference-cell as well as through a given sample cell. Again, it is vfrequently desirable to critically adjust the length of the sample cell for the analysis of a given constituent, or to particularly choose the windows of the different cells.

It is a particular feature of this invention that the apparatus described may be so constructed as to permit convenient insertion, or removal of particular filter, compensator, or sample cells.

The apparatus can readily be designed so that different cells may be removed and inserted while maintaining the necessary critical alignment essential in analysis apparatus of this type. Thus, it is convenient to provide standard lter and compensator cells containingr fluids adapted for the sensitization of the system for different components in different gas mixtures,v By this means the general apparatus illustrated in the y drawing may readily be adapted to the analysis of a wide variety of gas systems.

As indicated, the infra-red system heretofore described is advantageously combined with a mass spectrometer vl. As a specic example of this combination, let it be assumed thatit is desired to analyze a complicated gas containing several infra-red absorbing constituents and one or more gases which are not characteristically infra-red absorbent. In this case the infra-red portion of the apparatus can determined the percentages of infra-red constituents, while the mass spectrometer can be used to determine the concentration of the remaining constituents.

As is well known, certain gases of interest in the control of processes such as hydrogen, nitrogen, oxygen and others containing monatomic or diatomic molecules, possess no infra-red absorption properties. In this invention, these gases will be determined by the mass spectrometer, since their quantitative determination can be established by this means. This represents only one of three advantages in combining the mass and infra-red principles in a single analytical device. Another reason for this aforementio-ned combination resides in the fact that by combining both mass and infra-red principles, `data can be obtained to establish the percentages of both nitrogen and carbon monoxide. case, the carbon monoxide can be determined by infra-red absorption. By applying an appropriate factor to the value of the mass 28 value, which is due to the summation of the carbon monoxide and nitrogen, a value for nitrogen alone In this cases infra-.red is preferred (for'example-olefin types) and in other cases mass spectrometry` is preferred (total aromatics of each molecular weight range). Mass spectrometric principles are superior to infra-red, and would, therefore,

be used, whenever the presence of small amounts of a constituent with a higher molecular weight is to be detected in a mixture of. lower molecular Weight material.

By means of the apparatus describedl'i-ey tofore, it Ais possible to securel a 'total analysis of infra-red absorbing and non infra-red absorbing constituents of a gaseous mixture. In addition to the advantages listed, this procedure is valuable in providing information as to drift of the apparatus components. Thus, electronic changes or changes in radiation intensity occurring after a passage of time will be indicated by failure of the analysis results to total 100%.

What is claimedA is:

1. An improved detector assembly in apparatus for the multi-component infra-red determination f of gaseous mixtures consisting of a plurality of infra-red absorbent cells, said cells being arranged in pairs in the path of radiation through a plurality of gas samplevcells, one of each pair of absorbent cells being pneumatically connected to one side of a condenser microphone detector, while the other of the said pairs of absorbent cells is pneumatically connected to the other side of the said condenser microphone detector, andl o means to periodically control the impingement of can be established. This combining of appropulsating infra-red energy on each of the pairs of the said absorbent cells whereby the said detector periodically indicates anyy differential in infra-red energy reaching veach of the said pairs of cells.

2.Apparatus for the analysis of amulti-component gas sample comprising a plurality of sample cells, a source of infra-red radiation arranged to pass radiation through each ofsaid sample cells, a first plurality of infra-red absorbent cells arranged in the path of radiation through each sample cell, and a second plurality of infra-red absorbent cells arranged in a different portion of the path of radiation through each sample cell, a condenser microphone detector, fluid lines between said detector and said absorbent cells, and

means to periodically and sequentially permit im- Y pingement of radiation on the particular first and second absorbent cells in the path of radiation through each particular sample cell.

3. A multi-component analysis arrangement including in combination: a plurality of sample cells, a source Aof infra-red radiation arranged toY pass a beam of radiation through each of said sample cells, a pair of infra-red absorbent cells arranged in different portions of the beam of radiation passed through each sample cell, a condenser microphone detector, pneumatic connections between one cell of each pair of absorbent cells and one side of said detector and pneumatic connections between the other cell of each pair of absorbent cells and the other side 0f said detector, and means to sequentially permit said beams of radiation to impinge on eachA pair of absorbent cells.

4. The arrangement defined by claim 3 in which a pair of opticalcells are positioned in different portions of the said beam of radiation between each sample cell and each pair of absorbent cells.

5. The arrangement defined by claim 3 including means to periodically interrupt each of said 'i' l; beams of radiation to. provide pulsating infrared radiation.

JOHN J. HEIGL.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Journal of Scientiflc'lnstruments, December 1946,'page 293.

An Optical Acoustic Method of Gas Analysis,A by

5 P. J. Callisenl--Nature-February 1, 1947, page Infra-Red'lnstrumentation and Techniques', by V. Z. Williams. Review of Scientic Instruments, March 19`48,'pp.`135-1'778,C0py in Paten't/'Ofce Library. Y v v 

1. AN IMPROVED DETECTOR ASSEMBLY IN APPARATUS FOR THE MULTI-COMPONENT INFRA-RED DETERMINATION OF GASEOUS MIXTURES CONSISTING OF A PLURALITY OF INFRA-RED ABSORBENT CELLS, SAID CELLS BEING ARRANGED IN PAIRS IN THE PATH OF RADIATION THROUGH A PLURALITY OF GAS SAMPLE CELLS, ONE OF EACH PAIR OF ABSORBENT CELLS BEING PNEUMATICALLY CONNECTED TO ONE SIDE OF A CONDENSER MICROPHONE DETECTOR, WHILE THE OTHER OF THE SAID PAIRS OF ABSORBENT CELLS IS PNEUMATICALLY CONNECTED TO THE OTHER SIDE OF THE SAID CONDENSER MICROPHONE DETECTOR, AND MEANS TO PERIODICALLY CONTROL THE IMPINGEMENT OF PULSATING INFRA-RED ENERGY ON EACH OF THE PAIRS OF THE SAID ABSORBENT CELLS WHEREBY THE SIDE DETECTOR PERIODICALLY INDICATES ANY DIFFERENTIAL IN 